This invention relates to automatic control systems for the working tool of a civil machine.
In a known automatic blade control system a laser light beam is emitted from a laser light emitting device provided at a predetermined position for providing a reference height, while the laser light beam thus emitted is received and detected by a light receiving device fixedly provided at a predetermined position on the blade of a vehicle, for instance, thereby to obtain a height signal and the height of the blade is automatically controlled with the aid of the height signal. In another known system an inclination angle meter is provided on a predetermined position on the frame of a blade, and the height of the blade is automatically controlled on the basis of a deviation signal between the output signal of the inclination angle meter representative of an inclination angle with respect to the horizontal reference plane and the preset angle of the frame.
However, the blade height control system utilizing the laser beam is disadvantageous in that it is intricate in arrangement, and high in cost, and it is impossible to fully perform its functions in dusty places because the laser light is obstructed by dust.
In the blade height control system utilizing the inclination angle of the frame of the blade, it is required to precisely detect the inclination angle. In the case where the inclination angle meter utilizes gravity (as in the case of a pendulum type inclination angle meter), it is affected by a moment due to the inclination of the vehicle in the longitudinal direction thereof, and therefore the output signal of the meter is often erroneous. Accordingly, the blade height control system is liable to operate erroneously.
A land-leveling or earth-moving operation is generally performed when a civil machine advances, and upon reversing the civil machine merely returns to the position from which it started without doing any work. When the civil machine is reversed the work tool, e.g. a blade, is lifted or floated by a manual operation. In the reverse movement of the civil machine, the work tool is released from an automatic mode and is lifted or floated by a manual operation. Accordingly, a manual operation to lift or float the work tool is required every time the civil machine is reversed resulting in lowering of work efficiency.